Aluminium Unequal Leg Angles

IS 3909: Scope & Key Specifications

• Scope: Defines sectional properties and symbols for structural steel sections.
• Density: Steel density assumed as 2.7 gm/cm³ (Clause 2.7).
• Letter Symbols (Clause 3.1):

• Rounding Off: Final computed values must be rounded as per IS 2-1960, matching the precision of specified values.

flowchart LR
    A[Sectional Area (a)] --> B[Mass per unit length (M)]
    A --> C[Moments of Inertia (Ix, Iy)]
    C --> D[Section Modulus (Zx, Zy)]
    C --> E[Radius of Gyration (rx, ry)]
    D --> F[Design Calculations]

This scope sets the foundation for calculating section properties essential for structural design per IS 3909.

IS 3909 - Definitions: Key Symbols and Specifications

• a = Sectional area (cm² or mm²)
• M = Mass of the section per unit length (kg/m), based on density = 2.7 gm/cm³
• Ix, Iy = Moment of inertia about X-X and Y-Y axes respectively (cm⁴ or mm⁴)
• Iu, Iv = Maximum and minimum moments of inertia about principal axes U-U and V-V
• ex, ey = Distance of extreme fibre from X-X and Y-Y axes (cm or mm)
• Zx, Zy = Section modulus about X-X and Y-Y axes, calculated as:
  [ Z_x = \frac{I_x}{e_x}, \quad Z_y = \frac{I_y}{e_y} ]
• rx, ry, ru, rv = Radius of gyration about respective axes:
  [ r_x = \sqrt{\frac{I_x}{a}}, \quad r_y = \sqrt{\frac{I_y}{a}}, \quad r_u = \sqrt{\frac{I_u}{a}}, \quad r_v = \sqrt{\frac{I_v}{a}} ]

Notes:

• Density used for mass calculations = 2.7 gm/cm³ (Aluminium alloys)
• These definitions form the basis for structural calculations of aluminium sections per IS 3909.

flowchart LR
    A[Sectional Area (a)] --> B[Mass per unit length (M)]
    A --> C[Moments of Inertia (Ix, Iy)]
    C --> D[Section Modulus (Zx, Zy)]
    C --> E[Radius of Gyration (rx, ry)]
    D --> F[Extreme Fibre Distances (ex, ey)]

This concise summary helps in understanding and applying IS 3909 definitions for aluminium structural sections.

IS 3909 - Letter Symbols & Key Specifications

Clause 3.1: Letter Symbols

Additional Notes:

• Density of Aluminium: 2.7 gm/cm³ (Clause 2.7)
• Mass per unit length: ( M = a \times \rho ), where ( \rho = 2.7 \times 10^3 , kg/m^3 )
• Sectional properties for unequal leg angles are tabulated in Table 1 (Clause 5.1).
• Unequal leg angles may carry the ISI Certification Mark (Clause 8.2).

Summary Diagram of Section Properties

graph TD
    A[Sectional Area (a)]
    Ix[Moment of Inertia Ix]
    Iy[Moment of Inertia Iy]
    ex[Distance ex]
    ey

IS 3909: Materials - Key Formulas, Tables & Specifications

1. Material Density

• Density (ρ) = 2.7 gm/cm³ (Clause 2.7)

2. Section Properties (Clause 3.1)

Formulas:

[ Z_x = \frac{I_x}{e_x}, \quad Z_y = \frac{I_y}{e_y} ]

[ r_x = \sqrt{\frac{I_x}{a}}, \quad r_y = \sqrt{\frac{I_y}{a}} ]

3. ISI Certification (Clause 8.2)

• Unequal leg angles may bear ISI mark ensuring compliance with quality and inspection standards.

4. Units (SI Units Summary)

Summary Diagram: Section Properties

graph TD
    A[Sectional Area (a)]
    Ix[Moment of Inertia Ix]
    Iy[Moment of Inertia Iy]
    ex[Extreme Fiber ex]
    ey[Extreme Fiber ey]
    Zx[Section Modulus Zx = Ix/ex]
    Zy[Section Modulus Zy = Iy/ey]
    rx[Radius of Gyration rx = sqrt(Ix/a)]
    ry[Radius of Gyration ry = sqrt(Iy/a)]

    A --> Ix
    A --> Iy
    Ix --> Zx
    Iy --> Zy
    Ix --> rx
    Iy --> ry

IS 3909 - Dimensions and Tolerances for Aluminium Unequal Leg Angles

Key Points from Clauses:

• Clause 5.1: Dimensions and mass are per Table 1.
• Clause 5.1.1: Custom dimensions allowed by agreement.
• Clause 5.1.2: Sections without root radius (square fillet) allowed by agreement.
• Dimensional tolerances: As per IS 3965-1981.

Typical Dimensions Format (Clause 4.1 Example):

• ALU 80 x 60 x 6
  (Leg1 = 80 mm, Leg2 = 60 mm, Thickness = 6 mm)

Table 1: Dimensions, Mass & Sectional Properties (Excerpt)

Note: Refer IS 3909 Table 1 for full details.

Dimensional Tolerances (per IS 3965-1981):

• Thickness: ±0.3 mm
• Leg lengths: ±1.5 mm
• Straightness and twist: Within permissible limits as per IS 3965.

Summary:

• Use Table 1 for standard sizes and properties.
• Custom sizes and square fillets allowed by agreement.
• Follow IS 3965 for tolerances.

flowchart LR
    A[Start: Select Angle Size] --> B{Standard Size?}
    B -- Yes --> C[Use Table 1 Dimensions & Properties]
    B -- No --> D[Agreement between Purchaser & Manufacturer

IS 3909: Sectional Properties of Aluminium Unequal Leg Angles

Key Symbols (Clause 3.1)

Important Formulas

• Section modulus: [ Z_x = \frac{I_x}{e_x}, \quad Z_y = \frac{I_y}{e_y} ]

• Radius of gyration: [ r_x = \sqrt{\frac{I_x}{a}}, \quad r_y = \sqrt{\frac{I_y}{a}} ]

• Moment of inertia about principal axes: [ I_u = \text{max inertia}, \quad I_v = \text{min inertia} ]

Typical Section Example (Clause 4.1)

• ALU 80 × 60 × 6 (Unequal leg angle)
• Dimensions and properties are tabulated in Table 1 of IS 3909.

Summary Table Extract (Example)

(Refer IS 3909 Table 1 for full details)

flowchart LR
  A[

IS 3909: Packaging and Marking Key Points

• ISI Certification Mark (Clause 8.2):
  Unequal leg angles may be marked with the ISI mark, indicating compliance with IS 3909 under ISI's quality control and inspection system.

• Marking Requirements:
  The ISI mark assures the product meets the standard’s requirements, is produced under a defined quality system, and is subject to continuous ISI checks.

• Packaging:
  While IS 3909 does not specify detailed packaging formulas or tables, standard practice includes:

  • Protection against damage during transport
  • Clear marking of product details (size, length, weight, ISI mark) on packaging
  • Use of durable materials for packaging to prevent corrosion or deformation

• Density Reference (Clause 2.7):
  For weight calculations, use density = 2.7 g/cm³ (aluminium alloys typical).

Weight Calculation Formula for Aluminium Angles

[ \text{Weight (kg)} = \text{Length (m)} \times \text{Cross-sectional Area (cm}^2) \times 2.7 \times 10^{-2} ]

• Length in meters
• Cross-sectional area in cm²
• Density = 2.7 g/cm³ = 2.7 × 10⁻³ kg/cm³

Summary Diagram: Packaging & Marking Flow

flowchart TD
    A[Manufacture of Unequal Leg Angles] --> B[Quality Control & Testing]
    B --> C[ISI Certification Mark Approval]
    C --> D[Packaging]
    D --> E[Marking with ISI Mark & Product Details]
    E --> F[Dispatch & Continuous ISI Surveillance]

For detailed licensing and marking conditions, contact the Indian Standards Institution offices listed in the standard.

IS 3909 - Testing and Compliance Key Points

1. Rounding Off (Clause 0.7):

   • Test/analysis results must be rounded according to IS 2-1960.
   • Retain the same number of significant digits as specified in the standard.

2. ISI Certification Mark (Clause 8.2):

   • Unequal leg angles can bear the ISI mark, indicating compliance with IS 3909.
   • ISI mark assures production under strict quality control and continuous conformity checks.

3. Units & Definitions (International System of Units):

   Quantity	Unit	Symbol	Definition
   Length	metre	m	-
   Mass	kilogram	kg	-
   Force	newton	N	1 N = 1 kg·m/s²
   Pressure, stress	pascal	Pa	1 Pa = 1 N/m²

4. Density for Calculations:

   • Use 2.7 g/cm³ for aluminum density (Clause 2.7).

Summary Table for Compliance

flowchart LR
    A[Test/Analysis Result] --> B{Round off per IS 2-1960}
    B --> C[Retain significant figures]
    C --> D[Compare with Specified Value]
    D --> E{Pass/Fail}
    E -->|Pass| F[Allow ISI Mark]
    E -->|Fail| G[Reject/Retest]

Note: For detailed testing procedures, consult IS 3909 annexures or ISI guidelines.

Rounding Off Numerical Values as per IS 3909

• Reference Standard: IS 2-1960 governs rounding off rules.
• Key Rule: Final observed or calculated values must be rounded off to the same number of significant places as the specified value in the standard.
• Purpose: Ensures consistency and compliance verification in test/analysis results.

Summary of Rounding Off Rules (IS 2-1960):

Important Notes:

• Maintain significant figures consistent with the standard's specified value.
• Applies to all numerical results for compliance checking.
• Avoid excessive precision beyond the standard requirement.

flowchart TD
    A[Calculated/Observed Value] --> B{Check last digit to retain}
    B -->|<5| C[Round down]
    B -->|≥5| D[Round up]
    C --> E[Final rounded value with correct significant figures]
    D --> E

This ensures uniformity and clarity in reporting test and design data per IS 3909.

IS 3909 Key References:

• Density: 2.7 gm/cm³ (Clause 2.7) — used for mass and weight calculations.

• Letter Symbols (Clause 3.1):

• IS Units (SI) Table:

• ISI Certification Mark (Clause 8.2): Unequal leg angles may carry ISI mark ensuring compliance with ISI quality and inspection.

Summary Diagram of Section Properties

graph LR
A[Sectional Area (a)]